Bonded structures are incorporated into a variety of articles, including personal care products, medical garments, and industrial workwear garments, for example. Also, quite often, one or more components of an article are adhesively bonded together. For example, adhesives have been used to bond individual layers of an absorbent article, such as a topsheet (also known as, for example, the body-side liner) and backsheet (also known as, for example, the outer cover), together. Adhesives are also used to bond discrete pieces, such as fasteners and leg elastics, to the article.
Styrene block copolymer adhesives are often used to bond various materials to create bonded structures. Amorphous poly-alpha-olefin adhesives have been shown to provide slightly improved bond strengths relative to styrene block copolymer adhesives, particularly when bonding polypropylene film substrates. While the bond strengths of styrene block copolymer adhesives and amorphous poly-alpha-olefin adhesives may be sufficient for some uses, bond failure remains a problem in a number of applications.
In personal care products, such as diapers, bond strength is particularly important in the waist region and around the leg openings. These areas of disposable garments are exposed to considerable tension while the garments are being applied to or removed from a wearer, as well as while the garment is in use on a wearer. Consequently, the bonded structures in the waist region and leg openings of such garments are highly susceptible to bond failure. If bond failure between a topsheet and a backsheet occurs in the waist region, in particular, there is a likelihood that absorbent material positioned between the topsheet and the backsheet may escape from the garment, thereby causing a mess.
Bonding efficiency of adhesives requires adequate product bonding while minimizing such concerns as adhesive bleed-through, roll-blocking, machine contamination, and susceptibility to substrate deformation with hot-melt adhesives. Balancing these factors along with other factors such as cost is difficult. Additionally, it is difficult to achieve a bonded structure having sufficient bond strength when the structure includes certain substrates, such as polyethylene substrates or other low-energy olefin-surfaced substrates.
Burn-through is another potential problem that may occur during lamination or bonding processes. Preventive steps for avoiding burn-through typically include process changes such as reducing the adhesive add-on level, adjusting the temperature, installing new adhesive nozzles, adjusting a nozzle distance, or other processing changes. While effective in reducing burn-through, a reduced adhesive amount can have negative consequences on bond strength, and other process changes can be unrealistic due to adhesive rheology, high capital expenditures or lengthy machine down time.
There is a need or desire for a bonded structure having sufficient bond strength, particularly when the bonded structure includes one or more low-energy olefin-surfaced substrates. There is a further need or desire for a bonded structure that possesses sufficient bond strength that can be formed with minimal or no burn-through and without requiring process changes. There is yet a further need or desire for a cost-efficient bonded structure having sufficient bond strength. There is still a further need or desire for a personal care garment including one or more bonded structures or bonded components having sufficient bond strength.